The Inaugural Address. 



283 



Thus far, then, we have drawn out our subject to this point, that 

 at the bottom of a tranquil ocean calcareous mud was deposited by 

 the continual accretion of minute foraminiferous organisms, the vast 

 cemetery of whose dead structures was perpetually growing in thick- 

 ness as fresh millions upon millions of globigerine and other forami- 

 ferous creatures lived and died upon it. In this calcareous mud 

 would, of course, be imbedded any shells of shell-bearing animals 

 whose life was passed and ended in the supernatant ocean. At the 

 same time, and at the dark and tranquil depths at which this ocean- 

 floor lay spread, the conditions were present for sponge life to be 

 luxuriant, and when one generation of sponges became overgrown, 

 or gave place to fresh successors in the struggle for life, admirable 

 conditions would be afforded by the perished or perishing organisms 

 for the adherence and the dialysis of colloid silica into their interior. 

 There it would adhere to their spiculse, which consist of silica, itself 

 in the colloidal condition. It would enter and ultimately fill the 

 whole canal -system of the sponge, and finally surround and seal it 

 with a silicious envelope of adherent matter, not, however, concealing 

 its general outline and form. The diatom — and desmid — shields 

 would be entangled in the mass, and the formation of a flint bed as 

 the result of this process continuing through a certain era of time 

 would be conceivable. 



Yes, conceivable : but only to be received as a true possible cause 

 of the mode in which chalk and flint have been formed if two further 

 requirements can be satisfied, viz., that the sea-water contains silica 

 in solution to an appreciable amount, and that the separate formation, 

 whether contemporaneous or successive, of the calcareous rock and 

 the silicious flint-bed can find a reasonable explanation in the con- 

 ditions that must, or that with probability might, have prevailed at 

 the profound depth of that ocean-floor, from 10,000 to 15,000 feet 

 below the region to which the last traces of light could reach. To 

 the first of these questions the answer has been given by Forchammer, 

 who found in sea- water one part of dissolved silica in thirty thousand 

 to fifty thousand parts of the water. In fact, the existence of 

 swarms of minute vegetable organisms secreting silicious shells or 

 shield- cases in mid-ocean is its sufficient answer. But an abundance 



